凝固条件对钢锭中沟槽偏析影响的研究

 钢锭中形成沟槽偏析的传热条件不仅与凝固冷却速度有关,而且取决于轴向温度梯度G_A与径向温度梯度G_R之比。等比值G_A/G_R增大,形成较好的轴向顺序凝固,则有利于偏析的减轻,可通过不同条件下凝固区域高度H的变化来分析。在液固两相区,表示自然对流特性的每数采用经达西公式修正的G~D_r准则。高度H愈小,G_r~D也愈小,因而形成沟槽偏析的枝晶间液相对流也愈小,对流的减小有利于沟槽偏析的减轻。

RESEARCH ON THE INFLUENCE OF SOLIDIFYING CONDITIONS ON CHANNEL SEGREGATION OF STEEL INGOT

Thermal conditions forming channel segregation in a steel ingot depend not only on cooling rate but also on the ratio of axial temperature gradient, GA? to radial one, GR. If the ratio GA/GR increases, which is favourable to axial directional solidification, the segregation is well reduced. The reduction of the segregation is explained by the change of the height of mushy zone, H, under different conditions. Criterion GrD, modified by D'arcy law, is used to show the characteristic of natural convection in the mushy zone. The smaller the height H, the smaller the criterion GrD and the weaker the interdendritic, flow causing the channel segregation. Experimental results show that to make the steel ingot solidified directionally from bottom to top is one of the effective methods preventing the channel segregation.